In recent years, in the field relative to semiconductor manufacturing equipment or chemical manufacturing equipment, a gas dividing and supplying system has been employed in many cases with the enlargement of a process chamber, a reactor etc., and various types of gas dividing and supplying systems have been developed.
FIG. 12 shows an example of a conventional gas dividing/supplying apparatus that uses a thermal-type flow rate control device MFC (mass flow controller) or a pressure-type flow rate control device FCS, and gas G emitted from a gas supply source S is divided and supplied to a process chamber C and others through the thermal or pressure-type flow rate control device in the ratio of a divided flow rate Q1 to a divided flow rate Q2.
By the way, in the flow rate control devices that are provided to each of the divided flow passages, when gas starts to be supplied, an excessive flow-in of gas (overshooting phenomenon) is liable to easily occur in general, and especially in the thermal-type flow rate control device MFC, the occurrence of the overshooting phenomenon is inevitable.
In the thermal-type flow rate control device and a thermal-type mass flow sensor, variation of the zero point due to temperature and change in a detected flow rate caused by pressure in a flow regulating layer portion are relatively large and enhancement of flow rate control accuracy is hindered a lot.
Further, in case a gas flow rate for dividing and supplying is switched frequently, it is difficult to increase responsiveness of the divided flow rate control as it takes quite long time from when the divided flow rate control procedure including setting of a flow ratio (divided flow ratio) is started to when a stable control is established.
For example, based on results obtained by analyzing a cause of a gas overshooting phenomenon that occurs immediately after starting supply of gas by use of a gas supplying apparatus arranged as shown in FIG. 13, the present inventors have found that, in a gas supplying apparatus that uses the conventional thermal-type flow rate control device MFC, (a) most gas that causes the overshooting phenomenon is gas that stagnates in pipe passages L1 to L3 by which changeover valves V1 to V3 are connected to thermal-type flow rate control devices MFC1 to MFC3, respectively, and (b) the structure itself of each thermal-type flow rate control device MFC1 to MFC3 increases the stagnation of gas that causes the overshooting phenomenon.
In more detail, as shown in FIG. 14 that is a block diagram showing a basic structure of the conventional thermal-type flow rate control device MFC, gas flows in from the primary side is divided into gas portions flowing through a laminar flow bypass portion (flow regulating layer portion) 59 and a sensor bypass portion 60, and a mass flow rate of the gas is determined by a sensor 61 in the form of temperature change in ratio thereto, and the determined temperature change is converted into electric signals in a bridge circuit 62, and the resulting electric signals are output through an amplifier circuit 63 and others to a display 64 and to a comparison control circuit 65 as linear voltage signals. Meanwhile, set signal transmitted from outside is input from a setter 66 into the comparison control circuit 65, in which the difference between the aforementioned detected signal and the set signal is calculated, and the resulting signal difference is sent into a valve drive 67, which controllably open or close a flow rate control valve 68 in a direction in which the signal difference becomes zero. In the drawing, reference symbol 69 designates a power supplying portion.
Now, if a changeover valve V1 mounted on the secondary side is suddenly closed while the thermal-type flow rate control device MFC is in operation, the gas flowing through the sensor 61 comes to a standstill, and therefore the control system of the thermal-type flow rate control device MFC works transiently to increase the flow of gas, and the flow rate control valve 68 is opened accordingly. As a result, the gas pressure in the secondary-side line L1 rises, causing the gas stagnating therein to increase. Thereafter, when the changeover valve V1 is opened, the stagnating gas rushes into the chamber side through the changeover valve V1, causing the gas overshooting phenomenon.
Here, the occurrence of overshooting of gas in the gas dividing and supplying system inevitably causes a decrease in operating efficiency of semiconductor manufacturing facilities etc. or a decrease in quality of products. Therefore, it is necessary to prevent the occurrence of overshooting as much as possible.
On the other hand, in recent years, in this type of gas dividing/supplying apparatus, a desire to reduce the apparatus in size and in cost has been increased, and to meet such a desire, as shown in FIG. 15, a gas dividing/supplying apparatus has been developed that controls a gas flow supplied from a gas supply source 1 to have a total flow rate Q by use of the pressure-type flow rate control device FCS as a flow rate control system 4 and also controls gas flows of divided flow passages L1 to Ln to have divided flow rates Q1 to Qn with flow rate regulators 16, respectively.
In FIG. 15, reference symbol 1 designates the gas supply source, reference symbol 2 designates a pressure regulator, reference symbol 3 designates a pressure sensor, reference symbol 4 designates the flow rate control device (pressure-type flow rate control device FCS), reference symbols 5a and 5b designate pressure gauges, reference symbol 6 designates a thermal-type mass flow sensor (MFM), reference symbol 7 designates an electrically-operated valve, reference symbol 8 designates a valve driving portion, reference symbol 9 designates a vacuum pump, reference symbol 10 designates a throttle valve, reference symbol 11 designates a signal emitter, reference symbol 12 designates a PID controller, reference symbol 13 designates a process chamber, reference symbol 16 designates the flow rate regulator, reference symbol Sm designates a flow rate detecting signal, reference symbol Sa designates a flow rate setting signal, and reference symbol Sv designates a valve driving signal.
In the gas dividing/supplying apparatus of FIG. 15, the total flow rate Q of gas whose flow is controlled by the pressure-type flow rate control device (FCS) 4 is supplied to the divided flow passages L1, L2, and Ln in the divided flow rates Q1, Q2, and Qn, respectively. In other words, the divided flow rates Q1, Q2, and Qn of gas flowing through the divided flow passages L1, L2, and Ln, respectively, are supplied to the process chamber 13 in such a way that, for example, in the divided flow passage L1, the electrically-operated valve 7 is subjected to feedback control by means of the PID controller 12 according to the flow rate detecting signal Sm emitted from the flow sensor 6, and, as a result, the gas is controlled to have the divided flow rate Q1 corresponding to the flow rate setting signal Sa emitted from the signal emitter 11 and is supplied to the process chamber 13. In FIG. 15, the flow rate regulators 16 of the divided flow passages L2 to Ln are not shown.
However, also in the gas dividing/supplying apparatus of FIG. 15, a peak appears in the flow rate detecting signal Sm of the thermal-type mass flow sensor (MFM) 6, and so-called overshooting occurs in the gas having the flow rate Q1 flowing through the divided flow passage L1, for example, immediately after starting a gas admission (referred to as “when gas is admitted for supply”) into the divided flow passage L1 by inputting the flow rate setting signal Sa from the signal emitter 11 and by starting the pressure-type flow rate control device (FCS) 4. This significantly decreases accuracy in control of gas of the divided flow rate Q1.
The present inventors and others created a gas dividing and supplying system shown in FIG. 16 and repeat operation tests of the system as an approach for enhancing accuracy in control of gas of the divided flow rate Q1 by preventing the occurrence of overshooting that is caused immediately after starting a gas admission.
In more detail, FIG. 16 is a schematic view showing a configuration of the whole of the gas dividing and supplying system under the operation tests, and predetermined divided flow rates Q1 to Q4 of gas G are supplied to a large-sized reactor (e.g., a large-sized process chamber) 15 through divided flow passages L1 to L4 of four systems (n=4).
In FIG. 16, reference symbol 15 designates the large-sized reactor, reference symbol 16 designates the flow rate regulator, reference symbols 16a to 16d designate switching-type controllers, reference symbols Sv1 to Sv4 designate valve driving signals, reference symbols Sk1 to Sk4 designate valve opening degree control signals, reference symbols Sm1 to Sm4 designate flow rate detecting signals, and reference symbols Sa1 to Sa4 designate flow rate setting signals. In FIG. 16, the same reference symbol is given to the same component or the same member as in FIG. 15.
Referring to FIG. 16, in a steady state, gas G that is emitted from a gas supply source 1 and regulated by a pressure regulator 2 so as to have pressure of 300 to 500 KPa (abs) is controlled to have a desired set flow rate Q (e.g., 1000 to 3000 sccm) in a pressure-type flow rate control device (FCS) 4, and is supplied to the divided flow passages L1 to L4.
In the divided flow passages L1 to L4, a divided flow rate control command signal Ss is input to each of the switching-type controllers 16a to 16d in each of the flow rate regulators 16 from outside, and thereafter the valve driving signals Sv1 to Sv4 are respectively input to valve driving portions 8a to 8d from the switching-type controllers 16a to 16d and feedback divided flow rate control is performed, and then electrically-operated valves 7a to 7d are driven, and, as a result, gas flows having the divided flow rates Q1 to Q4 respectively corresponding to the flow rate setting signals Sa1 to Sa4 are supplied to the reactor 15. In other words, the valve driving signals Sv1 to Sv4 are subjected to feedback control by the flow rate detecting signals Sm1 to Sm4 emitted from the thermal-type mass flow sensors 6a to 6d, respectively, and, as a result, gas flows of the divided flow rates Q1 to Q4 are controlled to have set divided flow rates corresponding to the flow rate setting signals Sa1 to Sa4, respectively.
When the pressure-type flow rate control device (FCS) 4 supplies gas to the divided flow passages L1 to L4 in a state in which its flow rate is not controlled as in a case in which gas G temporarily stops being supplied and then is again supplied (i.e., when gas starts to be admitted), an opening control command signal Sp is first input to each of the switching-type controllers 16a to 16d, thereby maintaining opening control mode in which the switching-type controllers 16a to 16d perform the opening control of the electrically-operated valves 7a to 7d, respectively.
As a result, the valve opening degree control signals Sk1 to Sk4 are output to the valve driving portions 8a to 8d of the electrically-operated valves 7a to 7d from the switching-type controllers 16a to 16d, respectively, and each of the electrically-operated valves 7a to 7d is maintained at a fixed opening degree that is predetermined by the valve opening degree control signals Sk1 to Sk4 respectively without being completely opened (i.e., in a partially-closed state).
Later, when a state is reached in which flow rate control is performed by the pressure-type flow rate control device (FCS) 4 after a fixed time (e.g., 0.1 seconds to 1 second) elapses and gas having the controlled total flow rate Q is supplied, the divided flow rate control command signal Ss is input and the control mode of the switching-type controllers 16a to 16d is automatically (or manually) switched from a valve opening degree control state to a divided flow rate control state, and the divided flow rates Q1 to Q4 of gas flowing through the divided flow passages L1 to L4 are controlled to have set divided flow rates by means of feedback control based on the flow rate detecting signals Sm1 to Sm4 emitted from the thermal-type mass flow sensors 6a to 6d, respectively.
It should be noted that the valve opening degree control signals Sk1 to Sk4 for the opening control mode are pre-set appropriately, for example, based on the total flow rate in the pressure-type flow rate control device (FCS) 4 or the divided flow ratio (Q1/Q2/Q3/Q4).
Additionally, a cam drive type open-close valve whose driving source is a pulse motor is used as each of the electrically-operated valves 7a to 7d. 
FIG. 17 is a descriptive view of a configuration of the switching-type controller 16a, which is a main part of the flow rate control device, and reference symbol 17 designates a valve opening degree control command signal emitter, reference symbol 18 designates a divided flow rate control command signal emitter, reference symbol 19 designates a control switching mechanism, reference symbol 20 designates a valve opening degree control mechanism, reference symbol 21 designates a divided flow rate control mechanism based on the flow rate detecting signal Sm emitted from the thermal-type mass flow sensor 6, reference symbol 23 designates an input terminal of the flow rate detecting signal Sm, and reference symbol 24 designates an input terminal of the control switching signal Sx emitted from the pressure-type flow rate control device (FCS) 4.
When gas starts to be admitted (i.e., when the pressure-type flow rate control device (FCS) 4 supplies gas to the divided flow passages in a state in which its flow is not controlled), an opening control command signal Sp is firstly input from the valve opening degree control command signal emitter 17 to the valve opening degree control mechanism 20 through a terminal 22, and a valve opening degree control signal Sk, which is pre-set (e.g., 40% opening degree, 50% opening degree) is input from the valve opening degree control mechanism 20 to the valve driving portion 8, so that the electrically-operated valve 7 is maintained at a predetermined valve opening degree.
Of course, the valve opening degree control command signal emitter 17 is provided with an input mechanism of the valve opening degree control signal Sk.
When flow rate control is performed by the pressure-type flow rate control device (FCS) 4 and the total flow rate Q is controlled accordingly, a control switching signal Sx is input from the terminal 24 to the control switching mechanism 19, and this triggers the divided flow rate control command signal Ss to be emitted, then the divided flow rate control mechanism 21 is actuated accordingly, and feedback control of the valve driving signal Sv is implemented based on the flow rate detecting signal Sm emitted from the thermal-type mass flow sensor 6 and the flow rate setting signal Sa emitted from a flow rate setting mechanism attached to the divided flow rate control command signal emitter 18, and the divided flow is controlled by the electrically-operated valve 7.
Of course, switching to divided flow rate control by means of the divided flow rate control mechanism 21 may be performed also by automatically emitting the control switching signal Sx to the control switching mechanism 19 when a fixed time elapses after the actuation of the valve opening degree control mechanism 20 instead of inputting the control switching signal Sx from the input terminal 24, or may be performed by inputting the divided flow rate control command signal Ss to the control switching mechanism 19 from the divided flow rate control command signal emitter 18.
Preferably, the valve opening degree (i.e., the valve opening degree control signal Sk) is set in such a way that the valve opening degree of the electrically-operated valve 7 of when flow rate control is performed for a target flow rate (i.e., the set flow rate Sa) by use of the gas dividing/supplying apparatus is stored in a memory, and then the stored valve opening degree is pre-input and pre-set as the valve opening degree control signal Sk in the valve opening degree control mechanism 20.
Not like the conventional gas dividing/supplying apparatus shown in FIG. 15 that fully opens all the electrically-operated valves 7 in each of the divided flow passages when gas starts to be admitted, the gas dividing/supplying apparatus shown in FIG. 16 is capable of preventing the occurrence of overshooting at the time when gas starts to be admitted, which is caused by a delay in opening control of the electrically-operated valves 7, by maintaining the valves 7 at a predetermined valve opening degree in advance, and as a result, accuracy of divided flow rate control is enhanced significantly.
However, there are still many issues need to be solved left in the gas dividing/supplying apparatus of FIG. 16. For example, a pulse electrically-operated cam drive type valve is often used as the electrically-operated valve 7 as the valve is capable of control relatively large flow, however, in the pulse motor-operated cam drive type valve, a position of the valve element in fully-closed state is regulated with a spring mechanism with applying a fixed pressing load to a valve sheet, and therefore miniaturization and simplification of the electrically-operated valve 7 is not easily attainable due to the spring mechanism and positioning of the valve element in fully-closed state itself is troublesome. Additionally, sheet-leaking often occurs when the valve is fully-closed. (Japanese Published Unexamined Patent Application No. 2008-57594, Japanese Published Unexamined Patent Application No. 2011-117473 etc.)
Also, a so-called temperature drift easily happens in a zero point output value of the thermal-type mass flow sensor 6 and, as a result, accuracy of divided flow rate control fluctuates.
Further, the detected flow rate value is pressure-dependent and the detected flow rate of the thermal-type mass flow sensor 6 fluctuates generally based on pressure in the flow rate regulating layer. Therefore, there are issues of decrease in accuracy of opening degree control and divided flow rate control.
Moreover, the pressure in the flow rate regulating layer that brings the smallest amount of error in the detected flow rate varies with each of the thermal-type mass flow sensors. As a result, under reduced-pressure environment, such as 100 Torr or under, an issue of decreased divided flow rate control accuracy of each of the divided flow passages L1 to Ln is caused by the difference among the pressures in the flow rate regulating layers of the thermal-type mass flow sensors.
Furthermore, PID control parameters for the switching-type controllers 16a to 16d, which are main parts of the divided flow rate control devices, are all set as fixed values and the divided flow rate controls are conducted by the fixed PID control parameters whether the total flow rate Q is high or low, and as a result, control responsiveness and control accuracy are not enhanced because the PID control parameters are not the most suitable for controlling.
Also, all the electrically-operated valves 7a to 7d are controlled simultaneously as well as concurrently to have predetermined opening degrees based on the valve driving signals Sk1 to Sk4 that are suitably set according to the total flow rate Q or the divided flow ratio (Q1/Q2/Q3/Q4). Therefore, the controls of the opening degree interfere mutually and the controls easily become unstable, and as a result, it takes longer time for the controls to be stabilized. This lowers responsiveness of the divided flow rate control and the control responsiveness may not be enhanced.